Navigation assistance method based on anticipation of linear or angular deviations

ABSTRACT

A method for assisting in the navigation of an aircraft comprises steps of calculating and displaying a linear deviation on a first linear section and an angular deviation on a second angular section. The method comprises a step of calculation of an anticipated deviation of the aircraft, expressed linearly or angularly, projected to a time DT, characteristic of a reaction time of the aircraft, and of a statistical error distribution associated with this anticipated deviation; and a step of calculation of a probability of exceeding a predetermined target deviation, by means of the anticipated deviation and of the statistical error distribution. The method also comprises a crew alert when the probability is above a predetermined threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to foreign French patent applicationNo. FR 1200754, filed on Mar. 13, 2012, the disclosure of which isincorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to a method for assisting in the navigation of anaircraft 9, making it possible to optimize the following of a targettrajectory, and more particularly a method intended to optimize themanoeuvres of the aeroplane in an approach phase to the runway of thearrival airport.

An ongoing increase in air traffic and in the resulting workload for thepilot has been observed for some years. The number of tasks to becarried out on board is increasing. The decision time is becomingshorter and shorter whereas meanwhile there is a general trend towardsreducing the number of crew members. Automated procedures, making itpossible to a certain extent to release the crew from routine tasks, arebecoming increasingly widely used.

The tracking of the approach procedures of an aircraft towards therunway of the arrival airport represents a particular issue in theaeronautic field. This flight phase is critical: although very short, itrepresents a predominant proportion of the accidents with loss of thecraft. Having to take into account increasingly stringent environmentalconstraints, seeking for example to reduce pollution or sound nuisance,is making the approach procedure increasingly complex and difficult.Efforts are being made for example to minimize the distances reservedfor take-off and landing, or efforts are being made to pass overdetermined areas with high accuracy, minimizing the nuisances and theirdispersions. Another object of the new approach procedures is toincrease the rate of take-offs and landings to make it possible toimprove the capacity of the runways or navigate with very strictpositioning constraints in the case of relief close to the runways.

BACKGROUND

Various systems exist for assisting a crew in the piloting of anaircraft, notably during an approach phase. Particularly well knownamong these systems are the flight management systems, called FMS,schematically represented in FIG. 1 and comprising the followingfunctions:

-   -   location LOCNAV, identified 1: making it possible to locate the        aircraft by means of various geolocation tools or instruments        (GPS, GALILEO, VHF radio beacons, inertial units),    -   flight plan FPLN, identified 2: making it possible to input the        geographic elements forming the skeleton of the route to be        followed (departure and arrival procedures, way points, etc.),    -   navigation database NAVDB 3: making it possible to construct        geographic routes and procedures from data included in the bases        (points, beacons, interception or altitude legs, etc.),    -   performance database PRF DB 4: containing the aerodynamic and        engine parameters of the craft,    -   lateral trajectory TRAJ 5: making it possible to construct a        continuous trajectory from points in the flight plan, observing        the aeroplane performance levels and the containment        constraints,    -   predictions PRED 6: making it possible to construct an optimized        vertical profile compatible with the lateral trajectory,    -   guidance GUIDANCE 7: making it possible to guide, in the lateral        and vertical planes, the aircraft on its 3D trajectory, while        optimizing the speed,    -   digital data link DATALINK 8: making it possible to communicate        with the control centres, the airlines and the other aircraft.

In a typical approach phase as represented in FIGS. 2.a, 2.b and 2.c, anaircraft 9 seeks to follow a target trajectory 10 to reach a landingrunway 11. Generally, an approach phase comprises a first partconsisting of one or more “linear” sections 12 followed by a final“angular” section 13 converging towards a touchdown point 14, generallysituated close to the runway threshold 11. The final angular section 13is possibly followed by one or more linear sections 12 in the case of ago-around phase for an interrupted approach, also referred to as “MissedApproach”. On a linear section 12 as represented in FIG. 2.b, a lineardeviation 15 represents the distance separating an estimated position 16of the aircraft 9 and a desired position 17 on the target trajectory 10.The linear deviation 15 can be expressed by a lateral component and avertical component.

On an angular section 13 as represented in FIG. 2.c, an angulardeviation 18 represents the angle formed at the touchdown point 14,between the target trajectory 10 and a straight line D1 joining thetouchdown point 14 to the estimated position 16 of the aircraft 9. Theangular deviation 18 can be expressed by a lateral component and avertical component.

In the known systems, the aim is to minimize the linear deviation on alinear section. Along a linear section produced with a navigationperformance requirement, or RNP, standing for “Required NavigationPerformance”, the requirement is to keep the linear deviation 15 below alimit value. When the difference exceeds the limit value, the systemprovides for alerting the crew to enable it to decide on the correctivemeasures to be performed.

Along a linear section, the known systems propose to the crew, by meansof a human-machine interface, or HMI, graphic representation means,commonly called “monitoring” means, that make it possible to track thenavigation performance. In particular, the known systems propose atracking of the navigation performance on a linear section conforming toa current standardization, in particular the standard ICAO PBN Manual,doc 9613.

According to this standardization, a linear deviation 15 is graphicallyrepresented, as schematically represented in FIG. 3, on a first lateraldeviation axis 21 and a second vertical deviation axis 22. This iscalled linear monitoring 20, the representation of a linear deviation15, expressed laterally 23 and vertically 24, on the two deviation axes21 and 22. The linear deviation 15 is represented on the lateraldeviation axis 21 according to a lateral scale 25, called RNP, and onthe vertical deviation axis 22 according to a vertical scale 26, calledV-RNP, by means of a cross 27 symbolically representing the aircraft 9.

According to this standardization, when the aircraft 9 is positioned onthe target trajectory 10, it appears centred on each of the scales,lateral 25 and vertical 26; a deviation thus being able to be positiveor negative for each of the deviation axes 21 and 22. The equivalentdistance between two RNP or V-RNP graduations is variable, for exampleaccording to the approach phases, the linear sections, the flightconditions or the aircraft type. Typically, in a navigation performedwith a required navigation performance RNP, an alert will be transmittedto the crew when a linear deviation greater than 2 RNP graduationsoccurs.

As an example, in an approach phase, a tracking of the navigationperformance of “RNP 0.3” type may be required. The distance between twoRNP graduations is then equal to 0.3 nautical miles, and the laterallinear deviation should be centred on the trajectory with a maximumtolerance of plus or minus 1 nautical mile, corresponding to plus orminus 2 RNP, a threshold from which an alert is transmitted to the crew.It will be recalled that a nautical mile, also called NM, is a unitcommonly used by the person skilled in the art in the aeronauticalfield, 1 nautical mile corresponding to 1852 metres. The InternationalCivil Aviation Organization (ICAO) defines standards at internationallevel; in particular, the RNP values of 4 NM, 1 NM, 0.3 NM or 0.1 NM arethe reference values used worldwide. The principle of the navigationassistance method according to the invention applies however to any RNPvalue.

On the final “angular” section, the aim is to minimize the angulardeviation 18. In the known systems, a transmitting beacon arranged inproximity to the threshold of the landing runway 11 embodies thetouchdown point 14. The reception by the aircraft 9 of the signaltransmitted by the beacon then makes it possible to determine theangular deviation 18 of the aircraft 9 relative to its target trajectory10. Thus, the expression ILS (Instrument Landing System) navigationapplies, for an approach performed on an angular section in which theaim is to minimize the angular deviation 18. The navigation assistancemethod applies also to other types of angular approaches, such as, forexample, the MLS (Microwave Landing System) approaches which rely on awireless transmitting beacon, or, for example, the FLS (FMS LandingSystem) approaches which rely on a virtual beacon.

In the systems currently implemented, nothing is defined to guaranteethe maintenance of navigation performance on an angular section. Thesystems do not propose any sophisticated monitoring tool to enable thecrew to control the descent along an angular section, and havesufficient reaction time to manoeuvre the aircraft, in particular as theapproach continues and the cone of the deviations shrinks.

Moreover, the switchover between the two types of navigation, fromlinear to angular (and from angular to linear in the case of aninterrupted approach), is performed with no particular management of thetransition. It is possible to ensure the monitoring of the navigationperformance on the linear section, then when the aircraft 9 enters intothe angular section, the linear monitoring is interrupted, the crewobserves the angular deviation and decides on the corrective measures tobe applied, without the possibility of anticipation at the time of thetransition.

SUMMARY OF THE INVENTION

The invention aims to propose a navigation assistance method for anaircraft 9 in the approach phase that mitigates the implementationdifficulties cited above. The method seeks in particular to improve thecapacity to manoeuvre by the crew by anticipating the deviations of thecraft, in particular during an approach phase of the aircraft 9.

To this end, the subject of the invention is a method for assisting inthe navigation of an aircraft comprising steps for calculating anddisplaying:

-   -   a linear deviation, for the aircraft in approach phase towards        an arrival airport on a first section, called linear section;        the linear deviation representing a distance separating an        estimated position of the aircraft and a desired position on a        target trajectory; the linear deviation being able to be        expressed by a lateral component and a vertical component,    -   an angular deviation, for the aircraft in approach phase towards        an arrival airport on a second section, called angular section;        the angular deviation representing an angle formed at a        touchdown point situated in proximity to the landing runway        threshold, between the target trajectory and a straight line        joining the touchdown point to the estimated position of the        aircraft; the angular deviation being able to be expressed by a        lateral component and a vertical component.

The method also comprises the following steps:

-   -   a calculation of an anticipated deviation of the aircraft,        linearly or angularly, projected to a time DT, characteristic of        a reaction time of the aircraft, and of a statistical error        distribution associated with this anticipated deviation,    -   a calculation of a probability of exceeding a predetermined        target deviation, by means of the anticipated deviation and the        statistical error distribution.

The method according to the invention makes it possible to facilitatethe piloting of the aircraft by the crew. In order to improve theresponsiveness of the crew, the method makes it possible, fromanticipated deviations, to transmit various alerts to the crew, or elseselect various manoeuvres or reconfigurations making it possible tooptimize the trajectory of the craft in its approach phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, and other advantages willbecome apparent, on reading the detailed description of the embodimentsgiven as examples in the following figures.

FIG. 1, already presented, represents a known navigation assistancesystem, commonly called FMS,

FIGS. 2.a, 2.b and 2.c, already presented, represent an approach phasemade up of a number of linear sections and one angular section,

FIG. 3, already presented, represents means for graphicallyrepresenting, or monitoring, a linear deviation, laterally andvertically,

FIG. 4 illustrates means for graphically representing, or monitoring, anangular deviation, laterally and vertically,

FIG. 5 schematically represents the navigation of an aircraft during anapproach phase on an angular section, and the characteristics useful tothe calculation for converting an angular deviation to an equivalentlinear deviation,

FIG. 6 illustrates means for graphically representing the linear orangular deviations, called unified monitoring,

FIG. 7 schematically represents the navigation of an aircraft during anapproach phase containing curvilinear portions,

FIG. 8 schematically represents the principle of calculation of ananticipated deviation and of an associated error, represented for anaircraft in the approach phase on an angular section,

FIG. 9 illustrates means for graphically representing current andanticipated deviations and statistical error distributions which areassociated therewith,

FIG. 10 represents a schematic diagram of the navigation assistancemethod according to a first embodiment of the invention,

FIG. 11 represents a schematic representation of the navigationassistance method according to a second embodiment of the invention.

In the interests of clarity, the same elements will be given the samereferences in the different figures.

DETAILED DESCRIPTION

FIG. 4 illustrates means for graphically representing, or monitoring, anangular deviation, laterally and vertically. On the same principle asfor a linear deviation, described in FIG. 3, representing an angulardeviation 18 of the aircraft 9 on a lateral deviation axis 31 and avertical deviation axis 32 is envisaged.

There are a number of methods for establishing an angular deviation,notably according to the transmitting beacon type which embodies thetouchdown point. Whatever the method considered, it is possible todetermine an angular difference between the estimated position 16 of theaircraft 9 and its desired position 17 on the target trajectory 10.

The angular deviation 18 is represented by a lateral component 33 and avertical component 34 on two angular scales, lateral 35 and vertical 36.When the aircraft 9 is positioned on the target trajectory 10, itappears centred on each of the scales, lateral 35 and vertical 36; anangular deviation 18 can thus be positive or negative on each of thedeviation axes 21 and 22. The angular scales 35 and 36 comprisegraduations, commonly referred to as “dots”, corresponding to apredetermined angle value; this predetermined value generally beingdependent on the distance separating the aircraft 9 from the landingrunway 11. FIG. 4 represents means for graphically representing anangular deviation 18, or angular monitoring 30, making it possible torepresent, on the lateral 31 and vertical 32 deviation axes, the lateralangular deviation 33 and the vertical angular deviation 34 of theaircraft 9 by means of a rhomboid 37 symbolizing the aircraft 9,positioned on the angular scales, lateral 35 and vertical 36.

Thus, the navigation assistance method comprises steps for calculatingand graphically representing:

-   -   a linear deviation 15, for the aircraft 9 in approach phase        towards an arrival airport on a linear section 12; the linear        deviation representing the distance separating the estimated        position 16 of the aircraft 9 and the desired position 17 on the        target trajectory 10; the linear deviation 15 being able to be        expressed by a lateral component 23 and a vertical component 24,    -   an angular deviation 18, for the aircraft 9 in approach phase        towards an arrival airport on an angular section 13; the angular        deviation 18 representing the angle formed at the touchdown        point 14 situated in proximity to the landing runway threshold        11, between the target trajectory 10 and the straight line D1        joining the touchdown point 14 to the estimated position 16 of        the aircraft 9; the angular deviation 18 being able to be        expressed by a lateral component 33 and a vertical component 34.

FIG. 5 schematically represents the navigation of an aircraft 9 duringan approach phase on an angular section, and the characteristics usefulto the calculation for converting an angular deviation into anequivalent linear deviation.

Along the angular section, an angular deviation 41 is defined as theangle formed at the touchdown point 14, between a target trajectory 44and a straight line D2 joining the touchdown point 14 to an estimatedposition 42 of the aircraft 9. The orthogonal projection of theestimated position 46 of the aircraft 9 on the target trajectory 44corresponds to a desired position 43 of the aircraft 9. The distanceseparating the touchdown point 14 and the desired position is referenced45. A linear deviation 46 of the aircraft 9 corresponds to the distanceseparating the estimated position 42 and the desired position 43.

In these conditions, the knowledge of an angular deviation 41, forexample established by means of a wireless receiver picking up thesignal transmitted by a transmitting beacon, and of the distance 45, forexample established by means of the functions of location 1, ofconstruction of the target trajectory 5 and 6, and of guidance 7 of theaircraft, makes it possible to calculate an equivalent linear deviation46.

According to the invention, the navigation assistance method comprises astep of conversion of the angular deviation 41 into an equivalent lineardeviation 46, observing the following mathematical relationship:Dev=D*tan(Alpha)in which Dev represents the linear deviation 46, D represents thedistance 45 and Alpha represents the angular deviation 41.

According to the same principle, it is possible to determine a lineardeviation equivalent to the “dot” angle corresponding to a graduation onthe angular scale represented on FIG. 4. In other words, it becomespossible to represent, on a linear scale, a projection of an angulardeviation. On a linear section, a “dot” graduation corresponds to an“RNP” deviation and the scale remains identical as long as the RNPrequirement does not change. On an angular section, the scale changes asa function of the distance 45. The more the aircraft 9 approaches thetouchdown point 14, the tighter the scale becomes.

According to the invention, the navigation assistance method comprises astep of conversion of an angular deviation into an equivalent lineardeviation, according to a similar principle. Knowing the lineardeviation and the distance 45, for example by means of the functions oflocation 1, of construction of the target trajectory 5 and 6, and ofguidance 7 of the aircraft 9, the method determines an equivalentangular deviation by means of the mathematical relationship (i) whichhas already been described. This conversion makes it possible, forexample, to project a linear deviation onto a linear go-around sectionequivalent to a determined angular deviation on the final angularsection. It also becomes possible to force an angular guidance beforethe capture of the signal transmitted by the transmitting beacon.

Thus, the method comprises a step of conversion of an angular deviation41 into an equivalent linear deviation 46, and, conversely, theconversion of a linear deviation 46 into an equivalent angular deviation41, observing the following mathematical relationship:Dev=D*tan(Alpha)in which Dev represents the equivalent linear deviation 46, D representsa distance 45 between the touchdown point 14 and the desired position 43on the target trajectory 10, and Alpha represents the angular deviation41.

Advantageously, the navigation assistance method makes it possible totrack, all along the approach phase, a navigation performance, by meansof a deviation that can be represented independently on a linear orangular scale. As an example, it is possible to ensure the tracking ofperformance linearly, during the last linear section and during thetransition to the final angular section, by means of an equivalentlinear deviation determined by calculation on the basis of an angulardeviation. In a second stage, the crew can decide to switch over to adisplay of the deviations angularly, after the necessary manoeuvres onentering the angular section have been carried out. According to thesame principle, it is possible, in the case of an interrupted approach,to project a navigation performance onto the linear go-around section,by calculation on the basis of the measured angular deviation.

FIG. 6 illustrates graphic representation means according to theinvention, called unified monitoring 50, making it possible to display adeviation of the aircraft 9 all along an approach phase. The unifiedmonitoring 50 comprises a lateral deviation axis 51 and a verticaldeviation axis 52. A deviation of the aircraft 9 is represented by meansof a lateral deviation 53 positioned on the lateral deviation axis 51provided with a graduation scale 55, and of a vertical deviation 54positioned on the vertical deviation axis 52 provided with a graduationscale 56.

Advantageously, it is possible to choose, for each of the deviation axes51 and 52, between a linear graduation scale (as represented in FIG. 6)and an angular graduation scale (according to a graphic representationsimilar to that of FIG. 4 which has already been described). It willalso be possible to consider representing a combined scale, including,for each deviation axis, a linear scale and an angular scale. When alinear scale is selected, for example for the lateral deviation axis 51,it is possible to represent on this axis an angular deviation of theaircraft 9 (represented by the rhomboid in FIG. 6), previously convertedinto an equivalent linear deviation by the calculation means describedpreviously. It is also possible to select a different scale for each ofthe two deviation axes 51 and 52; for example, the scale 55 of thelateral deviation axis 51 being linear and the scale 56 of the deviationaxis 52 angular.

Advantageously, the unified monitoring 50 comprises, for each of thedeviation axes, lateral 51 and vertical 52, means for selecting thescales 55 and 56, linear, angular or combined. The selection can be mademanually for each of the deviation axes 51 and 52 by the crew, or can beperformed automatically by means of a number of criteria dependent onthe flight conditions.

In a preferred implementation of the invention, a first criterionprovides for switching over from a linear display to an angular displayon the two axes, as soon as one of the two axes switches over to angularmode. A second criterion provides for switching over from a lineardisplay to an angular display when the distance separating the aircraft9 from the landing runway 11 is below a predetermined threshold. A thirdcriterion provides for switching over from a linear display to anangular display as soon as the aircraft 9 receives a signal from thetransmitting beacon.

Advantageously, the graduations of the linear and angular scales of thelateral 51 and vertical 52 deviation axes correspond to a requirednavigation performance level. The graduations can be adapted to variablerequirement levels during the flight of the aircraft 9, according to thesame principle as described in FIG. 3 for the tracking of navigationperformance linearly. Thus, it is possible to select, for example forthe linear scales, graduations conforming to the currentstandardization, in particular the RNP and V-RNP scales. It becomespossible to ensure a tracking of the navigation performance, for exampleof “RNP 0.3” type, all along an approach phase, on a linear section andon the final angular section.

The navigation assistance method according to the invention isparticularly advantageous because it makes it possible to track thenavigation performance all along an approach phase, with nodiscontinuity between the different sections covered, both linear andangular.

FIG. 7 schematically represents the navigation of an aircraft 9 duringan approach phase containing a curvilinear trajectory.

A target trajectory 61 comprises a curvilinear portion 62 between thetouchdown point 14 and the desired position 63 of the aircraft 9 on thetarget trajectory 61. The desired position 63 corresponds to theorthogonal projection of the aircraft 9 on the target trajectory 61. Thelength of the curvilinear segment between the touchdown point 14 and thedesired position 63 is referenced 64. The linear deviation is referenced65.

It is possible to calculate, at each instant along this curvilineartrajectory, the distance 64 as well as the linear deviation 65, forexample by means of the functions of location 1, of construction of thetarget trajectory 5 and 6, and of guidance 7 of the aircraft 9. Fromthis calculation of the distance 64 and of the linear deviation 65, itis possible to determine and display an equivalent angular deviation 66,based on the distance 64 and the linear deviation 65. Thus, the unifiedmonitoring 50 can be applied in the case of an approach containing acurvilinear portion, and it becomes possible to carry out an angularapproach and a tracking of the navigation performance all along theapproach phase, on longilinear portions and on curvilinear portions.

Finally, it will also be possible to envisage integrating conditions forabandoning the unified monitoring 50 in the case where the trajectoryhas curvilinear portions with a radius of curvature below apredetermined threshold value; the accuracy of the linear projectionbecoming, in these conditions, too low.

FIG. 8 schematically represents the principle of calculation of ananticipated deviation DEV_ANT and of an associated statistical errordistribution ERR_ANT, represented for an aircraft 9 in approach phase onan angular section 13 converging towards a touchdown point 14.

In the figure, the aircraft 9 exhibits a deviation DEV_ACT relative to atarget trajectory 10. The deviation DEV_ACT can be expressed andrepresented independently angularly or linearly, by means of thefunctions described previously.

According to the invention, the navigation assistance method comprisessteps of calculating a statistical error distribution ERR_ACT associatedwith the deviation DEV_ACT. In a preferred implementation of theinvention, the statistical error distribution ERR_ACT is the sum of aplurality of error sources, each being taken into account in thecalculation by a statistical distribution. The statistical errordistribution ERR_ACT for example takes into account the errors linked tothe functions of location 1, of construction of the target trajectory 5and 6, or of guidance 7 of the aircraft 9. Thus, the method determines,at each instant, the deviation DEV_ACT and a statistical errordistribution ERR_ACT.

Thus, it is possible to determine, for a predetermined accuracyrequirement EXI_PREC, a range of the deviations 70 that observes thisaccuracy requirement. According to the same principle, it is possible todetermine, for a predetermined deviation range EXI_DEV, for examplecorresponding to a given required navigation performance, theprobability of presence of the aircraft 9 in the deviation rangeEXI_DEV.

According to the invention, the navigation assistance method comprises astep of calculating an anticipated deviation DEV_ANT, expressed linearlyor angularly, projected to a time DT, characteristic of a reaction timeof the aircraft 9, and a statistical error distribution ERR_ANTassociated with this anticipated deviation DEV_ANT.

Advantageously, the navigation assistance method comprises a step ofcalculating the time DT, based on:

-   -   a time DTH, representative of the human reaction time,        calculated by means of a plurality of parameters that can vary        during the flight, comprising at least a decision-taking time, a        time of engagement and of verification of a guidance mode, a        time of modification of the choices of the location means or a        time making it possible to place the aeroplane in a more stable        aerodynamic configuration,    -   a time DTA, representative of the manoeuvrability of the craft,        calculated by means of a plurality of parameters that can vary        during the flight, comprising at least one parameter        representative of the speed of the aircraft, one parameter        representative of the current manoeuvre for rejoining the target        trajectory or one parameter representative of the other current        navigation assistance methods.

In a preferred implementation of the invention, the time DT is equal tothe longest time between the human reaction time DTH and the timerepresentative of the manoeuvrability of the craft DTA. In analternative implementation, the time DT will be determined by means of asum of the times DTH and DTA, or even by means of a quadratic sum of thetimes DTH and DTA.

According to the invention, the navigation assistance method determines,for this time DT and by means of the known trajectory calculationfunctions, in particular the functions 6 and 7, an anticipated deviationDEV_ANT. A number of calculation means can be implemented to determinethe statistical error distribution ERR_ANT associated with theanticipated deviation DEV_ANT.

In a preferred implementation of the invention, the statistical errordistribution ERR_ANT is the sum of a plurality of error sources, eachbeing taken into account in the calculation by a statisticaldistribution. Advantageously, the error sources taken into accountcomprise at least the errors linked to the functions of location 1, ofconstruction of the target trajectory 5 and 6 or of guidance 7 of theaircraft 9.

An example of calculation of the statistical error distribution ERR_ANT,based on the expected performance of the functions of location 1, ofconstruction of the target trajectory 5 and 6, and of guidance 7 of theaircraft 9, is described below. In this preferred implementation, foreach of the axes (longitudinal, lateral and vertical) the error isdetermined in the form of a distribution Gaussian. The three errorsources are then modelled in the form of:

-   -   three vectors of the errors on the estimation of the bias:        -   EB_loc: 3D vector of the bias of the location functions 1            (longitudinal, lateral and vertical)        -   EB_traj: 3D vector of the bias of the target trajectory            construction functions 5 and 6        -   EB_guid: 3D vector of the bias of the functions of guidance            7 of the aircraft 9    -   a matrix of the errors on the estimation of the drifts ED,        including crossed terms between axes (three-dimension square        matrix)    -   three standard deviation vectors of the errors:        -   S_loc: 3D vector of the standard deviation of the errors on            the location functions 1        -   S_traj: 3D vector of the standard deviation of the errors on            the target trajectory construction functions 5 and 6        -   S_guid: 3D vector of the standard deviation of the errors on            the guidance functions 7 of the aircraft 9.

The statistical error distribution ERR_ANT expressed as an overall 3Derror vector is then determined by a function of the individual errorsERR_ACT, EB_LOC, EB_traj, EB_guid, ED, S_loc, S_traj, S_Guid. It ispossible, for example, to use the following relationship:ERR_ANT=ERR_ACT+EB_loc+EB_traj+EB_guid+ED*(DT DT DT)^(T)+N*(S_loc+S_traj+S_Guid)in which DT is the characteristic time defined previously, the vector(DT DT DT)^(T) making it possible to obtain, by multiplication with theED matrix, the 3D vector representing the errors on the drifts projectedat the time DT. N, generally expressed as sigma, represents the expectedaccuracy on the calculated error.

It is also possible to use a relationship of the type:ERR_ANT=ERR_ACT+SQRT(EB_loc²+EB_traj²+EB_guid²)+ED*(DT DT DT)^(T)+N*(S_loc+S_traj+S_Guid)in which SQRT corresponds to the square root function of the termsbetween brackets; this last relationship being particularly suited toindependent errors. Other mathematical relationships on these variablesare also possible according to the invention.

Thus, the method determines, at each instant, the anticipated deviationDEV_ANT and a statistical error distribution ERR_ANT. It is thenpossible to determine, for a predetermined accuracy requirementEXI_PREC, a range of the deviations 71 that observes this accuracyrequirement. According to the same principle, it is possible todetermine, for a predetermined deviation range EXI_DEV, for examplecorresponding to a given required navigation performance, theprobability of keeping, with the current trajectory, the aircraft 9within the deviation range EXI_DEV at the time DT.

FIG. 9 illustrates means for graphically representing the currentdeviation DEV_ACT and anticipated deviation DEV_ANT, and the statisticalerror distributions which are associated therewith, respectively ERR_ACTand ERR_ANT.

The deviation DEV_ACT of the aircraft 9 is expressed linearly by alateral component 81, represented graphically on a lateral deviationaxis 51 graduated by means of a linear scale 55, and by a verticalcomponent (not represented). As described previously, the deviationDEV_ACT could also be expressed and represented angularly, by means ofthe conversion functions described previously.

The anticipated deviation DEV_ANT, projected to the time DT, isexpressed by a lateral component 82 represented on the same scale as thecurrent lateral deviation 81.

According to the invention, the navigation assistance method comprises astep of graphic representation of the statistical error distributions,current ERR_ACT and anticipated ERR_ANT. Thus, for each of thedeviations 81 and 82, an error interval is determined, respectively 83and 84, by means of the statistical error distributions ERR_ACT andERR_ANT and for a predetermined accuracy requirement EXI_PREC.

The calculation and the graphic representation of an anticipateddeviation DEV_ANT and of an associated statistical error distributionERR_ANT are particularly advantageous in as much as this makes itpossible to give the crew a capacity to anticipate the trajectories ofthe aircraft 9. The crew has more time to react and decide on thecorrective measures to be applied.

These tools are also particularly suited to the unified monitoring 50described previously. In practice, it becomes possible, during atransition from a linear section to a final angular section, to maintainnavigation performance tracking all along the transition. It enables thecrew to anticipate the trajectory of the aircraft 9, and to evaluate,without discontinuity, the probability of maintaining, during thetransition and on the angular section, a navigation performance thatconforms to a given requirement, and, if appropriate, to anticipate thenecessary manoeuvres of the craft.

FIG. 10 represents a schematic diagram of the navigation assistancemethod according to a first embodiment of the invention.

According to this first embodiment, the navigation assistance methodcomprises the following three calculation steps carried out insuccession:

-   -   calculation 101 of the time DT, characteristic of a reaction        time of the aircraft 9,    -   calculation 102 of an anticipated deviation DEV_ANT for this        time DT and of an associated statistical error distribution        ERR_ANT,    -   calculation 103 of a probability PROB of exceeding a        predetermined target deviation EXI_DEV, for example        corresponding to a required navigation performance, by means of        DEV_ANT and ERR_ANT.

Advantageously, an alert 201 is transmitted to the crew when theprobability is above a predetermined ALERT threshold, for example 95%,99% or 99.99%.

Advantageously, the navigation assistance method as described in FIG. 10comprises one or more activation conditions, comprising at least one ofthe following conditions: the remaining distance to be covered to thetouchdown point 14 is less than a predetermined threshold distance, thetouchdown point 14 is transmitting a signal received by the aircraft 9.Similarly, the method comprises one or more deactivation conditions, soas to interrupt the calculation, for example when the aircraft 9 reachesthe landing runway 11.

Thus, the navigation assistance method is activated and deactivatedautomatically, and a confirmation of its activation and deactivation bythe crew can usefully be added.

FIG. 11 represents a schematic diagram of the navigation assistancemethod according to a second embodiment of the invention.

According to this second embodiment, the navigation assistance methodcomprises a list 100 of possible manoeuvres of the aircraft 9, and meansmaking it possible to evaluate the benefit of switching over to amanoeuvre in the list to improve the tracking of the navigationperformance.

The principle of the navigation assistance method can be described asfollows:

-   -   in a first phase, the calculations 101, 102 and 103 are carried        out in succession to determine a probability PROB of exceeding,        at the time DT, a predetermined target deviation EXI_DEV, by        means of the anticipated deviation DEV_ANT and of the associated        statistical error distribution ERR_ANT, that is to say with the        current trajectory of the aircraft 9,    -   in a second phase, the calculations 101, 102 and 103 are carried        out in succession, iteratively for each of the possible        manoeuvres in the list 100, so as to determine, in succession:        -   a time DTi, characteristic of the reaction time of the            aircraft 9, assuming that the crew switches over to the            manoeuvre concerned,        -   an anticipated deviation DEV_ANTi and a statistical error            distribution ERR_ANTI, determined for the time DTi and            assuming that the crew switches over to the manoeuvre            concerned,        -   a probability PROBi of exceeding, at a time DTi, the            predetermined target deviation EXI_DEV, assuming that the            crew switches over to the manoeuvre concerned.

From this calculation, different interactions with the crew can be putin place, to enable it to optimize the tracking of the navigationperformance, for example by deciding to switch over to one of themanoeuvres in the list 100.

Thus, a first alert 201 can be transmitted to the crew when theprobability PROB determined for the current trajectory is above thepredetermined ALERT threshold, for example 95%, 99% or 99.99%. A secondalert 202 can be transmitted to the crew when, at the end of thecalculation, all the manoeuvres exhibit a probability PROBi above thepredetermined ALERT threshold.

Advantageously, the navigation assistance method comprises means 203 forsuggesting to the crew to switch over to an alternative manoeuvre of theaircraft 9, which exhibits a probability PROBi less than the probabilityPROB calculated with the current trajectory.

Advantageously, the means 203 make it possible to suggest to the crew toswitch over to an alternative manoeuvre of the aircraft 9 that exhibitsa probability PROBi below a predetermined ALERT threshold.

Advantageously, the means 203 comprise means for selecting the manoeuvreproposed to the crew, comprising at least one of the following selectioncriteria: the first manoeuvre having been the subject of the calculationof probability PROBi below the predetermined ALERT threshold isproposed, the manoeuvre which exhibits the probability PROBi closest tothe predetermined ALERT threshold is proposed, the manoeuvre whichexhibits the lowest probability PROBi is proposed.

Advantageously, the list of manoeuvres 100 comprises at least theswitchover to alternative location functions 1, the switchover toalternative target trajectory construction functions 5 and 6, or theswitchover to alternative guidance functions 7, including, for example,the switchover to an automatic piloting mode. The list of manoeuvres 100can also include the transmission, automatic or on demand from the crew,of specific alert code or of standardized digital messages to otheraircraft or to air traffic control at the arrival airport; thistransmission being carried out by means of various devices such as, forexample, a transponder.

Advantageously, the navigation assistance method as described in FIG. 10comprises one or more activation conditions, comprising at least one ofthe following conditions: the remaining distance to be covered to thetouchdown point 14 is less than a predetermined threshold distance, thetouchdown point 14 is transmitting a signal received by the aircraft 9.Similarly, the method comprises one or more deactivation conditions, soas to interrupt the calculation, for example when the aircraft 9 reachesthe landing runway 11.

Thus, the navigation assistance method is activated and deactivatedautomatically, and a confirmation of its activation and deactivation bythe crew can usefully be added.

The invention claimed is:
 1. A method for assisting in navigation of anaircraft, the aircraft comprising at least one processor and at leastone display, the method comprising: calculating and displaying a lineardeviation for the aircraft in an approach phase towards an arrivalairport on a linear section, the linear deviation representing adistance separating an estimated position of the aircraft and a desiredposition on a target trajectory, the linear deviation expressed by alateral component and a vertical component; calculating and displayingan angular deviation for the aircraft in the approach phase towards thearrival airport on an angular section, the angular deviationrepresenting an angle formed at a touchdown point situated in proximityto a landing runway threshold located between a target trajectory and astraight line joining the touchdown point to the estimated position ofthe aircraft, the angular deviation expressed by a lateral component anda vertical component; calculating an anticipated deviation of theaircraft, expressed linearly or angularly, projected to a reaction timeof the aircraft; calculating a error distribution associated with theanticipated deviation; calculating a probability of exceeding apredetermined target deviation based on the anticipated deviation andthe error distribution; and comparing the probability to a predeterminedthreshold.
 2. The method according to claim 1, further comprisingalerting a crew of the aircraft when the probability is above thepredetermined threshold.
 3. The method according to claim 1, furthercomprising calculating the reaction time of the aircraft by: calculatinga time representative of a human reaction time based on a plurality ofparameters that vary during flight of the aircraft, the plurality ofparameters comprising one or more of a a decision-taking time, a time ofengagement and of verification of a guidance mode, a time ofmodification of choices of a locator, and a time for placing theaircraft in a more stable aerodynamic configuration; and calculating atime representative of maneuverability of the aircraft based on aplurality of parameters that vary during the flight of the aircraft, theplurality of parameters comprising one or more of a parameterrepresentative of a speed of the aircraft, a parameter representative ofa current maneuver for rejoining the target trajectory, and a parameterrepresentative of other current navigation assistance methods.
 4. Themethod according to claim 3, wherein the reaction time of the aircraftis equal to the longest time between the human reaction time and thetime representative of the maneuverability of the aircraft.
 5. Themethod according to claim 1, wherein the anticipated deviation and theassociated error distribution are calculated based on the reaction timeof the aircraft and on a plurality of error sources, each of the errorsources being taken into account in the calculation of the associatederror distribution.
 6. The method according to claim 5, wherein theerror sources taken into account in the calculation comprise one or moreof errors linked to functions of location, of construction of the targettrajectory, and of guidance of the aircraft.
 7. The method according toclaim 1, wherein, from a list of maneuvers of the aircraft, the methodfurther comprises determining, for each of the maneuvers in the list: asecond reaction time of the aircraft if a crew switches over to themaneuver concerned; a second anticipated deviation of the aircraft,expressed linearly or angularly, projected to the second reaction timeof the aircraft, and an error distribution associated with the secondanticipated deviation, if the crew switches over to the maneuverconcerned; and a probability of exceeding a predetermined targetdeviation, for the second anticipated deviation and the second errordistribution, if the crew switches over to the maneuver concerned. 8.The method according to claim 7, wherein the list of maneuvers comprisesone or more of a switchover to alternative location functions, aswitchover to alternative target trajectory construction functions, anda switchover to alternative guidance functions.
 9. The method accordingto claim 7, further comprising alerting the crew of the aircraft whenall of the maneuvers exhibit a probability above the predeterminedthreshold.
 10. The method according to claims 7, further comprisingproposing, to the crew of the aircraft, at least one maneuver exhibitinga probability below the predetermined threshold.
 11. The methodaccording to claim 10, further comprising selecting the at least onemaneuver to propose to the crew of the aircraft, the at least onemaneuver selected from the group consisting of the first maneuver havinga probability below the predetermined threshold, a maneuver having aprobability closest to the predetermined threshold, and a maneuverhaving the lowest probability.
 12. The method according to claim 1,further comprising, if the remaining distance to the touchdown point isless than a predetermined threshold distance, receiving, from thetouchdown point, a signal to activate the method.
 13. The methodaccording to claim 1, further comprising converting an angular deviationinto a linear deviation or converting a linear deviation into an angulardeviation, for calculating the anticipated deviation withoutdiscontinuity during a transition from the linear section to the angularsection.
 14. The method according to claim 1, further comprising:calculating an error distribution associated with a deviation, thedeviation being linear or angular, and displaying, to a crew of theaircraft, the deviation and the error distribution.